It would be nice to think that hydrogen could solve the world’s energy problems. It’s a great fuel: it burns with oxygen to produce heat and water. No by-products. No pollution other than the waste heat. That heat, itself, might be a problem, given enough time – but it’s far less of an evil in the immediate than burning fossil fuels.
There are, of course, a couple of gotchas. One is that hydrogen is the lightest known element and, as such, occupies significantly more volume than other fuels. It can be liquefied if it’s cooled to 33 degrees Kelvin above absolute zero – but to stop it boiling off, it has to be further cooled to 20.28 degrees Kelvin (−423.17 °F and −252.87 °C), and then kept there. That takes both energy and specialised storage facilities.
Liquid hydrogen is also a major hazard if it escapes. It’s cold enough to produce nasty burns, and while it’s non-toxic, the vapour can displace oxygen in an enclosed area, leading to asphyxiation. The vapour will also burn with oxygen – explosively – if there’s an ignition source. I have this vision of hydrogen-fuelled cars crashing and exploding the way petrol cars do in the movies after the special effects guys have cut loose on them.
More crucially, the energy calculation involved in isolating hydrogen is awkward. It’s easy enough to produce; zap water with enough electrical energy to overcome the molecular bonds, and it’ll split into oxygen and hydrogen. But that’s where the fun starts. It takes 237.13 kilojoules of electrical energy to split each mol of water, from which are produced 2 grams hydrogen and 16 grams oxygen. However, burning that hydrogen (with oxygen) to produce energy (and water) releases only 241.8 kilojoules.
The net gain, therefore, is minimal; and if you take into account the energy required to move and store the hydrogen (especially if liquid), the practical calculation turns to net loss – that is, it’ll take more energy to produce and store it than it will release when burned. And then we have to ask where the energy to produce and store the hydrogen comes from in the first place? If we’re not careful, it’ll involve burning coal – which means that hydrogen ceases to be the green fuel we imagine.
That’s why efforts are under way to find catalytic conversion that drops the input needed to crack. But that doesn’t solve the storage and safety issues.
My take? I think hydrogen is a great fuel – it’ll solve a LOT of problems and it has virtually no down-sides in terms of the environment. But we need to find practical ways of both making and storing it – methods that are safe, and which don’t simply burn more fossil fuels in the process. That is the challenge.